Sherlock Holmes decided while he was still relatively young to become what he terms a "consulting detective." This suits his talents, interests, and personality. He is a moody, solitary,, studious type of person who would find it difficult to work for anyone else. He creates a profession which enables him to be self-employed and even to work at home at hours of his own choosing. He is able to enjoy an ideal lifestyle because he solves most cases brought to him and therefore gets many lucrative cases.
Holmes is noted for his powers of deduction, but he has acquired all sorts of practical knowledge suitable to his profession, and he keeps extensive files and newspaper clippings which often prove useful in handling cases. He knows a lot about chemistry, anatomy, and other scientific subjects, some of which he studied at the university and others he has learned by himself. He is always reading, experimenting, and studying. He often tells his friend Watson that it is unwise to theorize without having sufficient facts, and he has said, "I cannot make bricks without straw." In other words, he is not a mere thinking machine.
In "The Red-Headed League," Holmes demonstrates various methods he uses in solving crimes. For instance, he knows a lot about Jabez Wilson's assistant because he spends so much time learning about the more important criminals in England, one of whom is John Clay, who is posing as Vincent Spaulding. Holmes is always traveling to the scenes of crimes or of probable crimes to make detailed inspections. In "The Red-Headed League" he examines the area around Wilson's pawnshop at Coburg Square and deduces that John Clay's objective is to dig a tunnel from the pawnshop basement to the nearby bank in order to commit a spectacular burglary.
“Let me see,” said Holmes, standing at the corner and glancing along the line, “I should like just to remember the order of the houses here. It is a hobby of mine to have an exact knowledge of London. There is Mortimer's, the tobacconist, the little newspaper shop, the Coburg branch of the City and Suburban Bank, the Vegetarian Restaurant, and McFarlane's carriage-building depot."
Holmes will commit all this information to his memory and perhaps find it useful to solving another case at some time in the future. It is because Holmes is always making such inspection trips that the stories are so interesting. The reader accompanies Holmes and Watson in his imagination and meets all sorts of interesting people and sees many interesting sights. In "The Red-Headed League," the reader meets Jabez Wilson, John Clay, and Mr. Merryweather the bank director. The Sherlock Holmes stories are always combinations of ratiocination and adventure--sometimes danger.
So Holmes uses his brain, but he uses all the resources available to that powerful brain, including memory, scientific knowledge, books, newspapers, and voluminous files, to acquire the facts he needs for his deductions. He is not an "armchair detective." He is very energetic when he needs to be. He has a vast storehouse of knowledge which is all useful to his profession, and he cares little about anything that does not have practical value for his work. He has published many monographs on highly specialized subjects. He becomes successful and famous over the years, so that he never has to worry about money and can take only the cases that interest him. "The Red-Headed League" is an example of a case he solves without collecting any fee. Another is 'The Adventure of the Speckled Band," and there are many others recorded by his friend and biographer, Dr. John Watson.